A new method and composition designed to eliminate problems associated with seepage loss and lost circulation of synthetic and oil based drilling fluids during drilling operations. More particularly, the method involves injecting a mixture into the well bore and the lost circulation zone, and the mixture forming a barrier within the well bore to prevent further loss of fluids.
Drilling fluids, or drilling muds as they are often known, are generally slurries of clay solids or polymers used in the drilling of wells in the earth for the purpose of recovering hydrocarbons and other fluid materials. Typically, a drilling mud is circulated down through the drill pipe, out the drill bit, and back to the surface through the annulus between the drill pipe and the borehole wall. Drilling fluids generally may include one or more of the following materials: viscosifiers or suspending agents, weighting agents, corrosion inhibitors, soluble salts, seepage loss control additives, bridging agents, emulsifiers, lubricants and other additives as desired.
Oil-based drilling fluids can be comprised of oils, including for example, diesel, poly alpha olefins, mineral oils, propylene glycol, methyl glycoside, modified esters and ethers, and the like and mixtures thereof, and invert emulsions of oil in which water is dispersed in an oil-based mediuim Oil based drilling fluids can be comprised entirely of oil, or more commonly, may contain water ranging in concentration from 50% up to 50%. In such a mixed oil and water system, water becomes the internal phase and is emulsified into the oil, i.e., oil becomes the external phase.
Drilling fluids can have a number of functions, including but not limited to, lubricating the drilling tool and drill pipe which carries the tool, providing a medium for removing formation cuttings from the well, counterbalancing formation pressures to prevent the inflow of gas, oil or water from permeable or porous formations which may be encountered at various levels as drilling continues, preventing the loss of drilling fluids into permeable or porous formations, and holding the drill cuttings in suspension in the event of a shutdown in the drilling and pumping of the drilling mud. Drilling fluid additives can form thin, low permeability filter cake that can seal openings in formation penetrated by the bit and act to reduce the unwanted influx of fluids and loss of the drilling fluids to permeable formation. The filter cake forms when the drilling fluid contains particles that are approximately the same size as the pore openings in the formation being drilled.
For a drilling fluid to perform the desired functions and allow drilling activities to continue, the drilling fluid must remain in the borehole. Frequently, undesirable formation conditions are encountered in which substantial amounts, or in some cases, practically all of the drilling fluid may be lost to the formation. Drilling fluid can leave the borehole through large or small fissures, or fractures in the formation or through a highly porous rock matrix surrounding the matrix.
Because fluid loss is a common occurrence in drilling operations, drilling fluids are typically formulated to intentionally seal porous formation during drilling in order to stabilize the borehole and control fluid loss. However, formations are frequently encountered that are so porous as to increase the loss of drilling fluids beyond an acceptable limit despite the use of traditional lost circulation additives. In extreme situations, when the borehole penetrates a fracture in the formation through which most of the drilling fluid may be lost, drilling operations may be stopped until the loss circulation zone is sealed and fluid loss to the fracture is reduced.
U.S. Pat. No. 3,701,384 Routson et al. discloses a method of sealing permeable areas in a formation by plugging the pores with a solid material. A slurry of finely divided inorganic solids is injected into the formation together with an aqueous colloidal dispersion of a water-insoluble metal hydroxide in dilute aqueous solution of an organic polymeric polyelectrolyte, preferably containing a high molecular weight polyacrylamide or hydrolyzed polyacrylamide. At low concentrations, between 0.01 and 0.2 percent by weight, the dissolved polymer causes the suspended solids to flocculate, thereby blocking pores in the formation. The tested inorganic solids included finely ground asbestos fibers and magnesium oxide. However, due to its carcinogenic nature, asbestos is undesirable for widespread commercial use.
U.S. Pat. Nos. 4,683,949 and 4,744,419 to Sydansk et al. disclose a method for sealing permeable areas in formations using polymers cross-linked in-situ. Both patents note that effective polymer/cross-linking agents must be supplied sequentially with great care to prevent the cross-linked polymer from setting up too early.
Various formation agents and additives are known in the art to form formation seals and/or filter cakes on the wall of a well bore. These include sugar cane fibers or bagasse, flax, straw, ground hemp, cellophane strips, ground plastics, ground rubber, mica flakes, expanded perlite, silica slag, ground fir bark, ground redwood bark and fibers, grape extraction residue, cottonseed hulls, cotton balls, ginned cotton fibers, cotton linters, and the like.
Generally, the use of cellulose fibers has been for control of seepage loss or lost circulation and differential sticking, rather than for the stabilization of shale formations. To prevent further seepage loss, a number of different cellulose materials have been added to drilling fluids in the prior art in an effort to reduce the permeability of the formation being drilled. Such prior known cellulose fiber materials can include fibrous, flake, and granular ground forms, and combinations thereof. Representative of such cellulose fibers include nut and seed shells or hulls, such as, for example, pecan, almond, walnut, peach, brazil, coconut, peanut, sunflower, flax, cocoa bean, cottonseed, rice, linseed, oat, and the like. See for example, House, et al., U.S. Pat. No. 5,004,553; Borchardt, U.S. Pat. No. 2,799,647; and Gockel, U.S. Pat. Nos. 4,460,052 and 4,498,995.
Of particular interest is the development of improved methods for preventing or minimizing loss of oil based or synthetic drilling fluids when low pressure formations are encountered in drilling operations or due to seepage in porous formations. While materials for the prevention of loss via seepage and circulation loss are well known for water based drilling muds, loss control additives for synthetic or oil based muds are particularly desirable due to the high costs associated with these replacement of these drilling fluids.